This invention relates to unsymmetrical t-aliphatic ("t"=tertiary) alpha-cyano-azo (and hydrazo) alkanes, their derivatives, processes for preparating same and processes utilizing such azo compounds as polymerization initiators.
Symmetrical azo compounds having a t-carbon atom joined to each azo nitrogen and symmetrical alpha, alpha'-dicyano-azo(and hydrazo) alkanes are known:
E. farenhorst and E. C. Kooyman, Rec. Trav. Chim. 72, 993 (1953). PA1 C. g. overberger et al., J. Am. Chem. Soc., 76, p. 2722, p. 6185 (1954); ibid. 75, 2078 (1953). PA1 T. e. stevens, J. Org. Chem. 26, 2531 (1961). PA1 S. f. nelson et al., J. Am. Chem. Soc. 88, 137, 143 (1966). PA1 H. wieland et al., Ann. 514, 145 (1934). PA1 D. y. curtin et al., J. Org. Chem. 21, 1221 (1956). PA1 C. g. overberger et al., J. Am. Chem. Soc. 80, 6562 (1958); ibid 81, 2154 (1959). PA1 D. c. iffland et al., J. Am. Chem. Soc. 83, 747 (1961). PA1 M. c. chaco et al., J. Org. Chem. 27, 2765 (1962). PA1 1. Unsymmetrical tertiary-aliphatic azoalkanes containing one alpha-cyano group per azo group and their derivatives as represented by the formula ##EQU4## where (R").sub.3 C- is a tertiary- (alkyl, cycloalkyl or aralkyl) radical where R" is alkyl, aralkyl or aryl, not more than one R" being aromatic; R.sub.1 and R.sub.2 are aliphatic or cycloaliphatic and together can form an alkylene diradical, and R.sub.2 can also be phenol or substituted phenyl; and Z is --CN, ##EQU5## PA1 a. Reacting a hydrazine, (R").sub.3 C--NH--NH.sub.2, with a ketone, ##EQU7## to form the hydrazone ##EQU8## reacting (A) with hydrogen cyanide at a temperature of from about 0.degree. to 80.degree.C. (preferably 10.degree.-80.degree.C., most preferably at 10.degree.-40.degree.C.) to form the hydrazo ##EQU9## and oxidizing (B) to form the corresponding desired azo product ##EQU10## where R", R.sub.1 and R'.sub.2 are as above defined. b. Reacting a hydrazine, (R").sub.3 C--NH--NH.sub.2 (preferably its acid salt (R").sub.3 C--NH--..sup.HX 2.sup.. HX where X is chlorine or bromine) with hydrogen cyanide or, preferably, an alkali metal cyanide (such as NaCN or KCN) and a ketone, ##EQU11## in water to form the hydrazo compound ##EQU12## and oxidizing (D) to the corresponding desired azo product ##EQU13## where R" is as above defined; R".sub.1 is methyl or ethyl; R".sub.2 is unbranched lower alkyl of 1-6 carbons, 2-carboxyethyl or (CH.sub.2).sub.1-3 OH; and R".sub.1 and R".sub.2 taken together can form the diradical --CH.sub.2 (CH.sub.2).sub.n CH.sub.2 -- where n is 2-5 and the diradical can also be substituted with lower alkyl groups except on both terminal methylene groups or on either terminal methylene group when the substituent is particularly bulky such as t-butyl. PA1 c. Reacting an alpha-haloazo compound ##EQU14## where X is chlorine, bromine or iodine (preferably chlorine or bromine), with MCN (where M is alkali or alkaline earth metal, preferably Na, K, Cs, or Ag) to give the desired azo product ##EQU15##
Unsymmetrical azo compounds where a t-carbon atom is joined to one azo nitrogen are known, none coming within the scope of this invention.
Other known azo compounds include unsymmetrical azonitriles (U.S. Pat. Nos. 2,778,818 and 3,282,912; and Canadian Pat. No. 724,144).
To the best of applicants' knowledge, the alpha-amido and alpha-amidoximo azoalkanes of this invention have not been previously reported.
2,2'-Azobis (isobutyronitrile), commonly called AIBN, is a commercially available compound of the type disclosed by C. G. Overberger and co-workers and has the structure: ##EQU3## AIBN has many shortcomings. It is a toxic solid. Moreover, the decomposition residue, 2,2,3,3-tetramethylsuccinonitrile, is a highly toxic solid (LD.sub.50 =30 mg/kg in ratg -- R. N. Harger et al., Federation Proceedings, 8205(1949)). Thus, it presents a toxic dusting problem when used in commercial operations and extreme precautions are required in its handling. It cannot be used as a blowing agent for the great majority of the plastic foam market due to the high levels of toxic residue left in the foamed product. It is insoluble in petroleum hydrocarbon solvents and possesses very low or limited solubility in most of the common organic solvents, especially those which are compatable with polymerization systems. This insoluble nature eliminates its use for many applications for which it would otherwise be suitable. It presents problems of metering, incorporation, mixing, dispersing, etc., and necessitates the use of a solvent that in many cases is not ideally suited for the particular application.
In general, the new compositions of the present invention eliminate these problems. The tertiary-(alkyl, cycloalkyl, bicycloalkyl or aralkyl) group on the one side of the azo function lowers the melting point of these compounds so that most of them are liquids or low melting solids which can be handled in the melted state. In addition, this tertiary group increases the solubility of these azos so that most of them are completely miscible with the common organic solvents including petroleum hydrocarbons. Thus, no dusting, metering, incorporating, mixing, and dispersing problems are encountered in using these new compositions. Also, the new compositions and their decomposition residues have chemical structures that suggest that they are, for the most part, significantly less toxic. Preliminary toxicological studies on the new compositions made in Examples I and II, set out later, indicate that they are significantly less toxic than AIBN. The less toxic nature of the new compositions coupled with their liquid and high solubility properties allows them to be used in many applications where AIBN cannot be used.
To the best of applicants' knowledge, none of the unsymmetrical alpha-cyano hydrazoalkanes of the subject invention have been previously reported, though the above-cited C. G. Overberger et al. and U.S. Pat. No. 2,778,818 disclose, respectively, symmetrical alpha, alpha'-dicyano-hydrazoalkanes and 2-(2'-hydroxyethyl-hydrazo)-2,4-dimethylvaleronitrile (primary alkyl group connected to the hydrazo group). Unsymmetrical t-carbon containing hydrazo compounds are reported by: Thiele, B. 28,2600; Angeli, Rome Atti Accad Tincei 26 I, 95 (1917); Thiele et al., Ann. 282,33 (1894); D. Neighbors et al., J. Am. Chem. Soc. 44, 1557 (1922).
Processes for preparing azonitriles have been reported by C. G. Overberger et al., J. Am. Chem. Soc. 71, 2661 (1949) and 80, 6562 (1958); Canadian Pat. Nos. 724,144 and 750,380; and U.S. Pat. Nos. 2,469,358; 2,778,818; and 3,282,912.
Since the subject compounds are novel, their use as initiators for vinyl polymerization, curing of resins, blowing agents, etc. have not been previously reported.